Research On Active Autofocus System Based On LED

Active autofocus technology can focus under low contrast and low light conditions because of its own signal transmitter,even for moving objects.It has the characteristics of high reliability and is widely used in industrial production.,instrument testing and other fields.For some small targets with unconventional surfaces and in the field of biological sample observation that is sensitive to light intensity,light-emitting diodes（LEDs）are perfect for their large divergence angles,low power,high luminous efficiency,and low heat dissipation.meet the needs of use.In this paper,two specific application examples of automatic computer refractometer and microscope focus drift correction system are used as the background,and an LED-based automatic computer refractor autofocus system and an LED-based microscope focus drift correction system are built respectively.From model construction,formula derivation to specific optoelectronic device selection,simulation analysis,the content of each part is described,and a system is built to test and analyze the actual performance to verify the correctness of the theoretical analysis.This paper has completed the following aspects of work:（1）Aiming at the analysis of the focusing process of the automatic computer refractometer and the special environment that needs to focus on the human eye,a small target with an irregular surface,an LED-based small target triangulation automatic focusing model is proposed.Autofocus formula.The selection and design ideas of key components in the system are introduced.Zemax Optic Studio software is used to simulate and simulate lens parameters and build a physical system to complete performance testing and error analysis.The focusing range and measurement accuracy of the autofocus system of the refractor meet the system requirements,and the correctness of the mathematical model and formula derivation is proved through experiments.（2）Aiming at the problem of focus drift during microscope observation and the problem of focus reference plane shift caused by switching immersion objective lenses,a focus drift correction system for microscopes based on LED is proposed,and the specific working principle of the system is analyzed and the hardware system is designed.A mathematical model is established and the formula for the correction of microscope focus drift and the relationship between the lens spacing of the offset adjustment module and the position of the imaging spot are theoretically deduced.（3）The selection and design ideas of key components such as light source,stepper motor,imaging lens,and image sensor in the LED-based microscope focus drift correction system were introduced,and Zemax Optic Studio software was used to optimize the design and simulate the optical path of the system.The simulation results of focus drift correction of objective lenses with different magnifications are analyzed to verify the feasibility of the system.（4）Build an LED-based microscope focus drift correction system to complete the performance test.Through the focusing test experiments and results analysis of different magnification objective lenses,the focusing range of the dry objective lens can reach 120μm,the focusing range of the water immersion objective lens is 24μm,the axial focusing accuracy when using the water immersion objective lens is less than 0.4μm,and the single-frame imaging speed can reach 1ms,to meet the application requirements of microscope focus drift system.The correctness of the mathematical model and formula derivation and the practicability of the microscope focus drift correction system are proved from the accuracy of the focus drift correction result and the focusing speed.